Photoacid generators for extreme ultraviolet lithography

ABSTRACT

A photoacid generator P +  A −  comprises (a) an antenna group P +  comprising atoms with high EUV photoabsorption cross-sections according to FIG.  1  and A −  anions; or (b) an antenna group P +  and A −  comprising anions with low photoabsorption cross-sections for EUV; or (c) an antenna group P + , comprising atoms with high EUV photoabsorption cross-sections according to FIG.  1  and A −  comprising anions with low photoabsorption cross-sections for EUV. Novel compounds comprise DTFPIO PFBuS, and DTBPIO CN5.

FIELD OF THE INVENTION

The present invention relates to polymer formulations used in extremeultraviolet (EUV) lithography and photolithography. More specifically,this invention relates to the field of Photoacid Generators (PAGs) usedin such polymer formulations.

BACKGROUND OF THE INVENTION AND RELATED ART

The dependency of the resolution of optical lithography on thewavelength and the numerical aperture has continuously been reflected bythe further development of corresponding exposure tools. Due to itssignificantly shorter wavelength, EUV lithography at 13.5 nm (92 eV) istherefore a promising technology for the next generation lithography. Ithas been demonstrated that chemically amplified resists (CAR) canachieve a resolution of 25 nm half-pitch line:space features withinterferometric EUV lithography (J. W. Thackeray, et al., Proc. SPIE6517, 651719 (2007)). However, source power and resist performances arefar from the set targets, thus leading to very slow photospeed. Forexample, the targeted source power for EUV manufacturing tools is 180 Wdelivered to the illuminator optics, while currently used sourcesstruggle to reach even intensities as low as 10 W at intermediate focus.Similar to the tool, EUV resists also need significant improvements toreach the targeted performance. For example, the targeted dose for aresolution of 32 nm is 10 mJ/cm² and the line width roughness is 1.7 nm.Currently investigated resist systems are far from these values. Due tothe present issues with EUV source power, resist sensitivity comprisesone of the main areas where improvement is required.

In chemically amplified resists (H. Ito, Adv. Polym, Sci. 2005, 172, 37;G. Wallraff, W. Hinsberg, Chem. Rev. 1999, 99, 1801), PAGs (J. Crivello,J. Polym. Sci. Part A: Polym. Chem. 1999, 37, 4241; H. Ito, C. G.Wilson, Polym. Eng. Sci. 23, 1012 (1983)) play a key role in imaging. Inconventional optical lithography, CAR formulations contain a nearlytransparent polymer matrix, a PAG and additional compounds, such as basequenchers, in smaller quantities. PAGs are non-acidic molecules thatabsorb photons and subsequently form acid via a photochemicaldecomposition. Acid is only formed in illuminated regions of the resistsand only in these regions, the resist polymer becomes soluble (usuallyafter baking) in basic developers.

Traditional, commercially available PAGs are for exampletriphenylsulfonium nonafluorobutanesulfonate (1; “TPS PFBuS”) orbis(4-tert-butyl-phenyl) iodonium nonafluorobutanesulfonate (2; “DTBPIOPFBuS”) having the following structure:

Some less commonly used, commercially available PAGs have less fluorinein the anion, such as TPS camphorsulfonate (3). However, thecorresponding acid, camphorsulfonic acid, is not as strong asnonafluorobutanesulfonic acid. Moreover, the cation is still not veryabsorbing at 13.5 nm.

Li et al., U.S. Pat. No. 7,235,342, col. 14, line 23 to col. 15, line 2disclose other typical PAGs used in the related art.

While the absorption of photons whose energy ranges from deepultraviolet (˜150 nm) to near infrared (−850 nm) by organic molecules,thus by PAGs, depends on the existence of certain chemical bonds, theabsorption of EUV light is characterized by photoabsorptioncross-sections that depend on the atomic composition of the compoundwhich varies by atom (FIG. 1).

It is known that EUV photons are also absorbed by the resist polymersand other components and not just by the PAG. (P. Dentinger, et al.,Proc. SPIE 3997, 588 (2000)). Under EUV irradiation, acid therefore maybe generated by secondary processes as well and not only by direct hitsof the PAG by the photons. (T. Kozawa, et al., Jpn. J. Appl. Phys. 31,4301 (1992)) However, literature reports also indicate a strong PAGstructure dependence on the acid generation efficiency in EUV light. (C.M. Szmanda, et al., J. Vac. Sci. Technol, B 17(6), 3356 (1999); T.Watanabe, et al., Jpn. J. Appl. Phys. 44, 5866 (2005))

Ionic PAGs have the general structure P⁺ A⁻, where P⁺ decomposes intoprotons (H⁺) upon irradiation with photons, while A⁻ remains unchangedand forms the acid H⁺ A⁻. In an efficient PAG, P⁺ therefore stronglyabsorbs the photons of interest, while A⁻ does not. In contrast, if A⁻absorbs too many photons, the acid generation efficiency may decreasebecause this decreases the amount of photons that could otherwise reachP⁺, or because A⁻ may decompose as a consequence of photon absorptionand therefore weakens the generated acid.

Commercially available PAGs, such as compounds 1, 2 and 3, commonly usedin polymer formulations for optical lithography and presently used inEUV lithography, do not have an EUV-optimized atomic composition. Forexample, in the commonly used PAG triphenylsulfoniumperfluorobutanesulfonate (1, TPS PFBUS), where Pa comprises thetriphenylsulfonium cation and A⁻ comprises the perfluorobutanesulfonateanion, the EUV photoabsorption cross-section of P⁺ is one order ofmagnitude lower than that of A⁻ (FIG. 2). In the case ofbis(t-butylphenyl)iodonium perfluorobutanesulfonate (2; DTBPIO PFBuS),the photoabsorption cross-section of P⁺ is still almost one order ofmagnitude lower than that of A⁻, though P⁺ contains the highlyEUV-absorbing iodine atom. To overcompensate lack of optimum EUVsensitivity, resist formulations with much higher PAG loadings thantypical for photolithographic applications are used. This can lead toincreased line edge roughness and high resist outgassing.

RELATED PATENTS AND U.S. PATENT APPLICATIONS

The following references include related art teachings:

-   -   O. Webster, U.S. Pat. No. 3,853,943;    -   R. P. Meagley, United States Patent Appl. 200510221220;    -   J. F. Cameron, U.S. Pat. No. 6,849,374;    -   K. Mizutani, et al., U.S. Pat. No. 7,232,640;    -   H. Nakao, et al., U.S. Pat. No. 7,214,465;    -   K. Mizutani, et al., European Patent Application EP 1338921;    -   S. Kanna, et al., U.S. Pat. No. 7,214,467;    -   S. Kanna, et al., U.S. Pat. No. 7,202,015;    -   K. Mizutani, et al., United States Patent Application        200710128547    -   Glodde et al., U.S. patent application Ser. No.

______ filed December ______, 2007, Attorney Docket No. FIS920070400US1(01400-12).

SUMMARY OF THE INVENTION

The foregoing indicates a need for an improved process for lithographicimaging, such as lithographic imaging using EUV irradiation (wavelength:<150 nm), particularly with respect to the photospeed obtained in suchlithographic image processing, and the formulation and use ofphotoresists having PAGs that are systemically optimized for absorptioncharacteristics required for most commonly used EUV photons (13.5 nm).

Accordingly, the present invention provides such a process andformulations that address these needs to not only provide advantagesover the related art, but also to substantially obviate one or more ofthe foregoing and other limitations and disadvantages of the relatedart, such as limited resist sensitivity, decreased acid generationefficiency of PAGs, and resist formulations with much higher PAGloadings than typical for photolithographic applications, and theconcomitant problems of bad line edge roughness (LER) and highoutgassing from the decomposed PAG molecules.

The description that follows sets forth features and advantages of theinvention apparent not only from the description but also by practicingthe invention. The written description, drawings, abstract of thedisclosure, and the claims, or as any of the foregoing may besubsequently amended will set forth additional features and advantagesof the invention and point out the objectives and other advantages ofthe invention showing how they may be realized and obtained.

To achieve these and other advantages, and in accordance with thepurpose of the invention as embodied and broadly described herein, theinvention comprises novel PAGs and an improved method for lithographicimaging using these PAGs, such as lithographic imaging using EUVirradiation, including such imaging that focuses on the photospeedobtained in such lithographic imaging processes. The present inventioncomprises the formulation and use of photoresists employing these PAGsthat are systematically optimized for absorption characteristicsrequired for EUV photons. Incorporation of these PAGs can increase theEUV photospeed of photoresists.

In one aspect, the present invention comprises a photoresist formulationcomprising:

(a) a resist polymer that is originally insoluble in aqueous, alkalinedevelopers, but becomes soluble in these developers upon reaction withacid, under conditions specific for the particular resist polymer;

(b) an ionic photoacid generator P⁺ A⁻, in which P⁺ contains atoms withhigh EUV photoabsorption cross-sections (“high” in a broader fashionmeans: atom-averaged EUV absorption cross-section>5×10⁵ cm²/mol; in anarrower fashion: >10⁶ cm² mmol, as calculated according to FIG. 1);examples; (see below in paragraph [0016]);

(c) a small amount of a base quencher, commonly used in the art (seeexample below in paragraph [0016]), with “small” referring to typicalPAG:base molar ratios anywhere from about 1:0.05 to about 1:0.2.

In the invention, including the aspect of the invention describedimmediately above, the resist polymer comprises one having an ethylenicbackbone. In one embodiment, the polymer comprises vinyl, acrylateand/or methacrylate monomeric units. The backbone of the polymercomprises a backbone free of unsaturated carbon bonds. In general, thephotoresist compositions of the invention are not limited to anyspecific imaging polymer. In one embodiment, the imaging polymer is onesuitable for use in EUV lithography (<150 nm; preferred 13.5 nm).

The imaging polymer may be either positive-tone or negative-tone and inone embodiment comprises a polymer capable of undergoing chemicaltransformations upon exposure of the photoresist composition to UV lightwhereby a differential in the solubility of the polymer in either theexposed regions or the unexposed regions is created. That is, the basepolymers employed in the present invention include any acid sensitivepolymer having acid sensitive side groups which can undergo catalyticcleavage in the presence of an acid generated by the inventive photoacidgenerator. In one embodiment, the polymers comprise those where at leastone of said sensitive side groups comprise polycyclic side groups.

The acid sensitive side groups of the polymers may contain a lactonemoiety or may be protected with various acid labile protecting groupsthat are conventional and well known in the art. Such protecting groupscomprise groups requiring high activation energy (e.g. tert-butyl esteror tert-butyl carbonyl groups), low activation energy (e.g. acetal,ketal, or silylethers), or a combination of both. In another embodiment,the imaging polymers comprisepoly([N-(trifluoromethysulfonyl)methacrylamide]-co-[2-methyl-2-adamantylmethacrylate]-co-[5-methacryloyloxy-2,6-norbornane carbolactone])(“S1”), poly([2-methyl-2-adamantylmethacrylate]-co-[5-methacryloyloxy-2,6-norbornane carbolactone](“MADMA-NORLAC”) and, for embodiments where 248 nm (KrF) radiation isused, poly(4-hydroxystyrene-co-tert-butyl acrylate) (65/35) (“ESCAP”).

The photoacid generator has the general structure P⁺ A⁻, where P⁺comprises an organic cation of the general structure R₁R₂R₃ Y⁺, or anorganic halonium cation of the general structure R₁R₂ X⁺, where Y⁺comprises O, S, Se, or Te, and X⁺ comprises a halogen, such as I, andR₁, R₂ and R₃ comprise aliphatic or aromatic moieties that can befurther substituted with common substituents, e.g., substituentscomprising atoms with a high EUV photoabsorption cross-section (in thesense as described herein) such as I, Se, F, O (examples for P⁺ includephenyl-bis(pentafluorophenyl)sulfonium (7.76×10⁵ cm²/mol, atom-avg.),diphenyl-pentafluorophenylselenium (5.48×10⁵ cm² μmol, atom-avg.) andbis(2,4,6-trifluorophenyl)iodonium (DTFPIO) (1.3×10⁶ cm²/mol,atom-avg.)); and A⁻ comprises the anion of a strong acid, for exampleR—SO₃ ⁻, where R comprises an aryl or alkyl group, unsubstituted or atleast partially substituted by common withdrawing atoms or moieties,such as fluorine; examples of such anions are triflate CF₃—SO₃ ⁻,perfluorobutanesulfonate (PFBUS) C₄F₉—SO₃ ⁻, perfluorooctanesulfonateC₈F₁, —SO₃ ⁻. The base quencher is selected from a group of compounds,comprising amines, t-butoxycarbonyl-protected amines or quaternaryammonium salts. Examples of such amines are triethylamine, pyrrolidine,trihexylamine; examples of t-butoxycarbonyl-protected amines aret-butoxycarbonyl-diethylamine, t-butoxycarbonyl-pyrrolidine, andt-butoxycarbonyl-dihexylamine; examples of quaternary ammonium salts aretetramethylammonium hydroxide, tetraethylammonium hydroxide andtetrabutylammonium hydroxide.

In another aspect, the present invention comprises a photoresistformulation comprising:

(a) a resist polymer that is originally insoluble in aqueous, alkalinedevelopers, but becomes soluble in the developer upon reaction withacid, under conditions specific for the particular resist polymer;

(b) an ionic photoacid generator P⁺ A⁻, in which in which P⁺ containsatoms with high EUV photoabsorption cross-sections (definition of “high”set forth herein) and A⁻ contains atoms with low EUV photoabsorptioncross-sections. (“low” means: atom-averaged EUV absorptioncross-section<5×10⁵ cm²/mol, as calculated according to FIG. 1;(examples set forth herein).

(c) a small amount of a base quencher, as defined in paragraph [0016].In these formulations, we employ a small amount of a base quencher whichmeans, e.g., an amount of a base sufficient to react with any acids thatmigrated into unexposed areas during post-exposure bake employed in aphotolithographic process according to the invention.

In the invention, including the aspect of the invention describedimmediately above, the resist polymer comprises polymers as describedherein. The photoacid generator has the general structure P⁺ A⁻, whereP⁺ comprises an organic cation of the general structure R₁R₂R_(3Y) Y⁺,or an organic halonium cation of the general structure R₁R₂ X⁺, where Y⁺comprises O, S or Se, X⁺ comprises a halogen, such as I, and R₁, R₂ andR₃ comprise aliphatic or aromatic moieties that can be furthersubstituted with common substituents, e.g., substituents comprised ofatoms with a high EUV photoabsorption cross-section (in the sense asdescribed herein), such as I, Se, F, 0 (examples for R₁R₂R₃X⁺ and R₁R₂Y⁺are described herein) and A⁻ comprises the anion of a strong acid,comprising atoms with low EUV photoabsorption cross-sections (definitionof “low” as described herein) such as C, H, N, S, B and selected fromthe group of peracceptor-substituted aromatic anions or carboranes(examples are pentacyanocyclopentadienide (4.76×10⁵ cm²/mol, atom-avg.),camphorsulfonate (3.20×10⁵ cm²/mol, atom-avg.), carborane C₂B10H₁₂ ⁻(1.09×10⁵ cm²/mol, atom-avg.)). Meagley, United States Patent Appl.2005/0221220, describes carboranes.

The base quencher is selected from a group of compounds, comprisingamines, t-butoxycarbonyl-protected amines or quaternary ammonium salts(examples are described herein).

In another aspect, the present invention comprises a photoresistformulation comprising:

(a) a resist polymer that is originally insoluble in aqueous, alkalinedevelopers, but becomes soluble in the developer upon reaction withacid, under conditions specific for the particular resist polymer;

(b) an ionic photoacid generator P⁺ A⁻, in which A⁻ contains atoms withlow EUV photoabsorption cross-sections (“low” as defined herein);

(c) a small amount of a base quencher (as defined herein).

In the invention; including the aspect of the invention describedimmediately above, the resist polymer comprises polymers as describedherein. The photoacid generator has the general structure P⁺ A⁻, whereP⁺ comprises an organic cation of the general structure R₁R₂R₃ Y⁺, or anorganic halonium cation of the general structure R₁R₂X⁺, where Y⁺comprises O, S or Se, X⁺ comprises a halogen, such as I, and R₁, R₂ andR₃ comprise aliphatic or aromatic moieties that can be furthersubstituted with common substituents; and A⁻ comprise the anion of astrong acid having atoms with low EUV photoabsorption cross-sections(definition of “low” as described herein); such as C, H, N, S, B(examples described herein). The base quencher is selected from a groupof compounds, comprising amines, t-butoxycarbonyl-protected amines orquaternary ammonium salts (examples as described herein).

Additional features, objectives, and advantages of the invention are setforth in, and will be apparent from this written description, or may belearned by practice of this invention and realized and obtained by thecompounds, compositions and processes generally, and as pointed out notonly in this written description, but also the claims that follow, theabstract of the disclosure and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying Figures where like reference numerals refer toidentical or functionally similar elements throughout the separate viewsare incorporated into this specification, which together with thedetailed description herein serve to further illustrate variousembodiments and to explain various principles and advantages of thepresent invention.

FIG. 1 shows photoabsorption cross-sections for EUV photons (13.5 nm; 92eV), based on data from the calculator athttp://henke.lbl.gov/optical_constants/pert_form.html.

FIG. 2 shows EUV photoabsorption cross-sections for selected PAGcomponents, averaged per atom of the corresponding component. Examplesof P⁺ cations shown in FIG. 2 are triphenylsulfonium (TPS),bis(4-tert.-butylphenyl)iodonium (DTBPIO), triphenylselenium (TPSe) andbis(2,4,6-trifluorophenyl)iodonium (DTFPIO). Examples of A⁻ anions shownin FIG. 2 are perfluorobutanesulfonate (PFBuS),bis(perfluorobutanesulfone)imidate (N4(3M)) andpentacyanocyclopentadienide (CN5).

FIG. 3 and FIG. 4 show EUV dose to clear measurements of commerciallyavailable PAGs compared to the novel PAGs of this invention. In FIG. 3,MADMA-NORLAC stands for the copolymer poly([2-methyl-2-adamantylmethacrylate]-co-[5-methacryloyloxy-2,6-norbornane carbolactone]). InFIG. 4, ESCAP comprises poly(4-hydroxystyrene-co-tert-butyl acrylate)65/35.

FIGS. 5 and 6 show E_(1/2) data relative to commercial PAGs (=1) and (a)photospeed in EUV is not related to speed at 248 nm or 193 nm, (b)support the concept that EUV specific PAGs have to be designed.

FIG. 7 shows EUV photospeed correlated with EUV absorption by the PAGcation, and further EUV photospeed increases when EUV absorption by thePAG cation increases.

DETAILED DESCRIPTION OF THE INVENTION

To achieve these and other advantages, and in accordance with thepurpose of this invention as embodied and broadly described herein, thefollowing detailed embodiments as examples are disclosed that can beembodied in various forms. The specific compounds, compositions,processes and structural details set out herein comprise a basis for theclaims and a basis for teaching one skilled in the art to employ thepresent invention in any novel and useful way. The terms, phrases andFigures are also set out herein to provide an understandable descriptionof how to make and use this invention.

The preset invention comprises novel photoacid generators to beformulated into polymer compositions that are useful in lithographicprocesses, especially when EUV photons are used. In carrying out thepresent invention, conventional materials and processing techniques canbe employed and, hence, such conventional aspects are not set forthherein in detail. For example, the selection of suitable resistpolymers, bases and solvents is conducted in a conventional manner. Onehaving ordinary skill in the art once aware of the present disclosurecould employ suitable formulation, coating and exposure techniqueswithout undue experimentation.

In another aspect, the invention comprises PAGs optimized for EUVphotoabsorption. In the structures described in greater detail below, P⁺is significantly higher absorbing for EUV photons; or A⁻ consists onlyof atoms with a low photoabsorption cross-section for EUV, while stillbeing an anion of a very strong acid; or a combination of the two. Theterms “high” and “low” photoabsorption cross-section for EUV, wherevermentioned in this section, refer to atom-averaged EUV absorptioncross-section>5×10⁵ cm²/mol and atom-averaged EUV absorptioncross-section<5×10⁵ cm²/mol, respectively, as calculated according toFIG. 1.

In the present invention, components of PAGs are strategically selectedfor absorption characteristics required for EUV photons. One set ofcomponents of such PAGs acts as an antenna for EUV photons and cancomprise atoms with high EUV photoabsorption cross-sections. Thiscomponent decomposes upon reaction with photons under formation of aproton, and this proton forms a strong acid by combination with anothercomponent of the PAGs. This other component of such PAGs which becomespart of the newly formed acid can comprise atoms with low EUVphotoabsorption cross-sections; or, as a combination, the set of PAGcomponents acting as antenna for EUV photons comprising atoms with highEUV photoabsorption cross-sections and the set of PAG componentsbecoming part of the newly formed acid comprising atoms with low EUVphotoabsorption cross-sections according to FIG. 1.

Formulation of such PAGs into photoresists leads to enhanced photospeedof the resists when irradiated with EUV photons, compared to photoresistformulations with conventional PAGs.

The PAG components acting as antennae for EUV photons comprises organiconium cations selected from organic chalconium cations of the generalstructure R₁R₂R₃Y⁺, where Y⁺ comprises oxygen (O), sulfur (S), selenium(Se), or tellurium (Te) and of organic halonium cations of the generalstructure R₁R₂ X⁺, where X⁺ comprises a halogen, such as iodine (I). Inthe onium cations, R₁, R₂ and R₃ comprise aliphatic or aromatic moietiesthat can be further substituted with common substituents, such ashalogens, such as fluorine (F) or iodine (I), alkyl, alkyloxy, aryl,aryloxy, nitro, cyano, halogen-substituted alkyl or halogen-substitutedalkyloxy, and the like.

This invention encompasses such onium cations that comprise atoms X⁺ orY⁺ and/or substituents R₁, R₂, R₃ characterized by a high EUVphotoabsorption cross-section. The other PAG component of the inventionis characterized as one that remains as a weakly coordinating and/ordelocalized anion upon completion of the photochemical decomposition ofthe herein described PAGs. Examples of such anions are organicsulfonates R₄—SO₃ ⁻(in which R₄ comprises perfluoroalkyl or substitutedor unsubstituted aryl or heteroaryl groups) and peracceptor-substitutedanions 4, 5, 6 or 7:

where E represents a strong electron-withdrawing substituent,particularly the cyano group CN. At least one substituent E can also berepresented by another group, including but not limited to hydrogen,alkyl, alkyloxy, alkyloxycarbonyl, nitro or a halogen. One example ofsuch peracceptor-substituted anions is compound 8, which corresponds tocompound 4 with all E represented by cyano groups (CN):

The synthesis and properties of this pentacyanocyclopentadienide anion(4) are described in the literature (O. Webster, J. Am. Chem. Soc. 1966,88, 4055; O. Webster, U.S. Pat. No. 3,853,943; H. E. Simmons, et al., J.Org. Chem. 1980, 45, 5113; C. Richardson, C. Reed, Chem. Common. 2004,706).

Such anions in conjunction with protons form very strong acids thatcomprise, e.g., sulfonic acid R₄—SO₃H (in which R₄ comprisesperfluoroalkyl or substituted or unsubstituted aryl or heteroarylgroups), carboranes and peracceptor-substituted cyclic organiccompounds, such as 4a, 5a, 6a or 7a, which are characterized by thegeneration of aromaticity upon removal of the one remaining hydrogenatom:

Calculations of the acids 4a, 5a, 6a, and 7a with E=CN(R. Vianello, Z.Maksic, Tetrahedron 2005, 61, 9381) have shown that all of these are—inthe gas phase—super acids (i.e., acids of greater acidity than 100%H₂SO₄) with pKa values ranging from −13 to −23. Therefore, anion 4 (andin some instances the anions of 6, 7 and 8 as well) is very wellsuitable for the application as PAGS, particularly for EUV due to thecomparably low photoabsorption of carbon and nitrogen, but has not yetbeen used as such.

An example of the cyclic, peracceptor-substituted organic anions towhich this class is not limited, comprises the group of compounds 4, 5,6, and 7, in which E comprises an electron-withdrawing group, such asthe cyano group (CN). However, the electron-withdrawing, group is notlimited to the cyano group (CN), but all E can be independent from eachother, and at least one group E can also be represented by an alkyl,alkyloxy, hydrogen, nitro, alkoxycarbonyl, halogen, aryl, aryloxy oraryloxycarbonyl group.

In a further aspect, the invention comprises ionic PAGs of the generalstructure P⁺ A⁻, where:

I-P⁺ comprises an organic sulfonium, selenium or halonium, comprisingiodonium, cation of the general structure R₁R₂R₃S⁺, R₁R₂R₃Se⁺ or R₁R₂X⁺,respectively, where R₁R₂R₃ comprise aliphatic or aromatic moieties thatcan be unsubstituted or substituted with common substituents, such ashalogens, comprising fluorine, alkyl, alkoxy, aryl, aryloxy, nitro,alkyl or aryloxo, or alkyloxy- or aryloxy carbonyl groups, X⁺ compriseshalogen; or, R¹ and R² comprise collectively a C₂-C₃₀ linear or branchedalkylene (CH₂)_(n) chain and R³ comprises at least one of Ar andAr—CO—CH₂—, where Ar comprises an aryl group, optionally substitutedwith common substituents, such as OH, branched, linear or cyclic alkylor branched, linear or cyclic alkyloxy; specifically in form of theS-aryl-tetrahydrothiophenium cation (9).

where Ar is an aromatic group, or a substituted aromatic group.

In one embodiment the substituents of the groups R₁, R₂, and R₃,comprise atoms with high photoabsorption cross-sections in EUV as shownin FIG. 1. However, such cation P⁺ can also have low photoabsorptioncross-section in EUV when used in conjunction with an anion A⁻ with lowphotoabsorption cross-section in EUV.

Additionally, A⁻ may comprise the anion of a very strong organic acid.Such acid in one embodiment comprises atoms with low photoabsorptioncross-sections in EUV as shown in FIG. 1. Generally, such anions cancomprise cyclic organic compounds, per-substituted withelectron-withdrawing groups E, in which the ring-protonation destroysaromaticity. Examples of this class of anions comprise compounds 4, 5, 6and 7 as follows:

where E comprises a strong electron-withdrawing substituent, and in oneembodiment this substituent comprises low photoabsorption cross-sectionin EUV, comprising the cyano group CN. However, the electron-withdrawinggroup is not limited to the cyano group (CN), but E can be the same ordifferent. Other substituents, E, comprise an alkyl, alkyloxy, hydrogen,nitro, alkoxycarbonyl, halogen, aryl, aryloxy or aryloxycarbonyl group.These anions with low EUV absorption are not limited to the anions 4, 5,6 and 7, but could be anions of carboranes and other art-known anions aswell that also exhibit low EUV absorption. R. P. Meagley, United StatesPatent Appl. 2005/0221220 gives examples of such carboranes.

Disclosed anions A⁻, however, can also comprise aliphatic sulfonates,comprising perfluoroaliphatic sulfonates, substituted or unsubstitutedarylsulfonates, when used in conjunction with a cation P⁺ that compriseatoms with high photoabsorption cross-section in EUV light.

PAGs P⁺ A⁻ of the invention comprise cations P⁺, atoms with highphotoabsorption cross-section in EUV, such as the above-mentionedsulfonium, selenium or iodonium cations comprising fluorine assubstituents of the groups R₁, R₂, and/or R₃, and of anions A⁻comprising atoms with low photoabsorption cross-section in EUV,comprise, e.g., such above-mentioned cyclic organic anions that aresubstituted with strong electron withdrawing groups, comprising e.g. CN.

II. Specifically, and in one embodiment, PAGs P⁺ A⁻, comprise:

1. P⁺ comprising;

a) a sulfonium cation, comprising,

b) a selenium cation, comprising;

c) an iodonium cation, comprising,

2. A⁻ comprises the anion of a very strong acid, comprising:

The compound

not only functions in PAGs used in lithographic methods that employ EUVradiation as the exposure radiation, but also is effective in opticallithography such as lithography using 248 nm exposure radiation, and 193nm exposure radiation as well.

For the PAGs in the combinations P⁺ A⁻ with P+=1a or 1c and A⁻=2b, P⁺comprises cations used in commercially available PAGs, and A⁻ comprisesan anion of a superacid that has very low EUV absorbance.

For the PAGs in the combinations P⁺ A⁻ with P⁺=1b or 1d and A⁻=2a, P⁺comprises cations of higher (1b) or extremely high (1d) photonabsorption in EUV, and A⁻ comprises an anion used in commerciallyavailable PAGs.

For the PAGs in the combinations P⁺ A⁻ with P+=1b or 1d and A⁻=2b, P⁺comprises cations of higher (1b) or extremely high (1d) photonabsorption in EUV, and A⁻ comprises an anion of a superacid that hasvery low EUV absorbance. It is intended that the foregoing descriptiondoes not include art known PAG compounds or their use in EUVphotolithography.

The above mentioned PAGs in II, have been synthesized, characterized andformulated into polymeric photoresists. Acid generation has beendemonstrated through titration experiments and dose-to-clear experimentsof both optical (248 nm, 193 nm) and EUV lithography.

In summary, this invention encompasses acid-forming PAG componentscomprising atoms or substituents R₄ or E that are characterized by a lowEUV photoabsorption cross-section.

EXAMPLES

The following examples illustrate embodiments of the invention.

Example 1

Materials synthesis (Bis(2,4,6-trifluorophenyl)iodoniumperfluorobutanesulfonate, 10 [DTFPIO PFBuS]): According to the method byBeringer et al. (J. Am. Chem. Soc. 81, 342 (1959)), 2 mmol (0.51 g)iodine and 6 mmol (1.3 g) KlO₃ were mixed in a 50 ml round-bottom flaskand stirred with 10 ml conc. H₂SO₄. The reaction was continued at roomtemperature, until the dark brownish color of iodine had completelydisappeared and a yellowish solid of (IO)₂SO₄ formed. Subsequently, 10mmol (1.3 g) of 1,3,5-trifluorobenzene was added to the (IO)₂SO₄suspension in H₂SO₄ and the mixture was stirred at 55° C. for 20 h. Thesolution was then added drop-wise to 100 ml H₂O and the precipitatefiltered off. The obtained aqueous solution ofbis(2,4,6-trifluorophenyl)iodonium hydrogensulfate was further extractedwith ether (1×) and benzene (1×). Subsequent addition of aqueoussolution of potassium perfluorobutanesulfonate to the aqueous reactionmixture gave a white, crystalline precipitate that was thoroughly washedwith water and dried in an oil pump vacuum for 16 h.

Example 2

Material synthesis (Bis(2,4,6-trifluorophenyl)iodoniumpentacyanocyclopentadienide, 11 [DTFPIO CN5]): To 0.45 g NaH (60% inmin. oil) in 35 ml dimethoxyethane was added 0.91 g methyl cyanoacetateunder N₂. Once hydrogen evolution had ceased, 2.83 g of2,3,5,6-tetracyano-1,4-dithiin, prepared according to the literature (C.Richardson, C. Reed, Chem. Commun. 706 (2004); H. E. Simmons, et al., J.Org. Chem. 45, 5113 (1980)), was added. The mixture was stirred at 110°C. for 30 min, then heated up to 160° C. until the solvent wasevaporated. Remaining traces of solvents were removed in oil pumpvacuum, until a dark brown, dry solid was formed. This solid wasdissolved in 100 mL of water, followed by addition of 5 mL conc. H₂SO₄.Filtration from the dark brown solids yielded a reddish solution thatwas discolored by addition of 2 mL of 30% H₂O₂ and heating to 80° C. for60 min. The obtained solution of sodium pentacyanocyclopentadienide wasthen cooled to room temperature and filtered; excessive H₂O₂ wasdestroyed with Na₂SO₃, while a strong acidic pH was maintained. Additionof an aqueous solution of bis(2,4,6-trifluorophenyl)iodoniumhydrogensulfate, prepared as in Example 1, gave a yellowish precipitatethat was filtered, dried and recrystallized from acetone/ether.

Example 3

Material synthesis (Bis(4-tert-butylphenyl)iodoniumpentacyanocyclopentadienide, 12 [DTBPIO CN5]): To an aqueous solution ofsodium pentacyanocyclopentadienide, prepared as described in Example 2,was added an aqueous solution of bis(4-tert-butylphenyl)iodoniumacetate. The obtained yellow is precipitate was filtered, dried andrecrystallized from acetone/ether.

Example 4

Formulation and film formation: A propyleneglycolmonomethylether acetate(PGMEA) solution of 10 wt % poly(4-hydroxystyrene-co-tertbutyl acrylate)(65/35; ESCAP), bis(2,4,6-trifluorophenyl)iodoniumperfluorobutanesulfonate (DTFPIO PFBuS), 10, in an amount equimolar to0.4 wt % TPS PFBuS and tetrabutylammonium hydroxide (TBAH) (basequencher; used in very small quantities to quench acid that migratesinto unexposed regions, thereby improving image quality) was prepared.TBAH was used in a PAG:TBAH=1.0.05 molar ratio. A silicon wafer (5″) wascoated with 0.8 nm AR3-600 (3000 rpm, then baking at 220° C. for 1min.), followed by coating with the resist solution (1400 rpm, thenbaking at 130° C. for 1 min). The obtained film thickness was 220 nm.

Example 5

Dose-to-Clear Experiment: EUV exposures were performed on an EQ-10M EUVlight source (Energetiq Technology Inc.), using Xe gasdischarge-produced plasma that provides 10 W into 2 pi in-band EUVirradiation (within 2% bandwidth). Long wavelength out-of-band radiationwas blocked by a Zr filter (thickness: 200 nm). A sample, consisting of5×¾ inch piece of a wafer, coated with a photoresist film prepared asdescribed in Example 4 was mounted at a 90° angle with respect to thebeam and was irradiated with an in-band EUV intensity of 2 mW/cm². Afterincremental steps of EUV exposure, the sample was baked at 120° C. for 1min, developed with 0.26 M tetramethylammonium hydroxide (TMAH) for 45 sand finally rinsed with de-ionized water. Function of the base used insuch developer solutions is to dissolve reacted, soluble resist polymer.The film thickness of the unexposed and exposes areas was measured on aNanoSpec (Model 4000; Nanometrics, Inc.). Dose to clear was 1.2 mJ/cm².

Example 6

Dose-to-Clear Experiment with Commercial PAG: A sample prepared asdescribed in Example 4 and exposed in the same fashion as described inExample 5 but containing commercially availablebis(4-tert-butylphenyl)iodonium perfluorobutanesulfonate (DTBPIO PFBuS)cleared at 4.5 mJ/cm². Atom-averaged EUV photoabsorption cross-sectionsfor the DTFPIO and DTBPIO cations are shown in FIG. 2.

Example 7

Dose-to-Clear Experiment: A sample is prepared and exposed in the samefashion as described in examples 4 and 5 but containingbis(2,4,6-trifluorophenyl)iodonium pentacyanocyclo-pentadienide (DTFPIOCN5), 11, cleared at 1.2 mJ/cm². Atom-averaged EUV photoabsorptioncross-sections for the CN5 and PFBuS anions are shown in FIG. 2.

Example 8

Dose-to-Clear Experiment: A sample is prepared and exposed in the samefashion as described in examples 4 and 5 but containingbis(4-tert-butylphenyl)iodonium pentacyanocyclo-pentadienide (DTBPIOCN5), 12, cleared at 1.2 mJ/cm².

Example 9

Dose-to-Clear Experiment: A sample is prepared and exposed in the samefashion as described in Examples 4 and 5 but containingpoly([2-methyl-2-adamantylmethacrylate]-co-[5-methacryloyloxy-2,6-norbornane carbolactone] andbis(2,4,6-trifluorophenyl)iodonium perfluorobutanesulfonate, 10, clearedat 10.0 mJ/cm².

Example 10

Dose-to-Clear Experiment with Commercial PAG: A sample prepared andexposed in the same fashion as described in Examples 9 but containingcommercially available triphenylsulfonium perfluorobutanesulfonatecleared at 20.0 mJ/cm².

Examples 9 and 10 describe experiments with a formulation comprising apolymer with higher protection ratio, which explains why bothdose-to-clear values are higher than in the other examples.

As noted before, the invention generally and specifically defines highEUV photoabsorption and low EUV photoabsorption, and when used in thiswritten description, high EUV photoabsorption and low EUVphotoabsorption refer to all definitions, and the general definitionsare included in addition to those instances where specific definitionsof high EUV photoabsorption and low EUV photoabsorption are given. Thecompounds of the invention also include various organic and othermoieties per se, but are also intended to include organic or othermoieties that can be further substituted with substituents; where theseorganic and other moieties, and/or substituents comprise inter alia,aryl groups, alkyl groups; halogens, such as fluorine (F) or iodine (I),as well as bromine (Br), or chlorine (Cl), alkyloxy, alkyloxo, aryloxo,arylcarbonyloxy, carboaryloxy, alkylcarbonyloxy, carbalkyloxy, aryloxy,nitro, cyano, halogen-substituted alkyl or halogen-substituted alkyloxy,substituted alkyl, alkylene, alicyclic, hydrocarbyl, cyclic alkyl(cycloaliphatic), hetero cycloaliphatic, aralkyl or alkaryl, alkoxy,acyl, acyloxy, alkylenoxy, such as defined inter alia by Allen et al.,U.S. Pat. No. 7,193,023, col. 3, line 51 to col. 6, line 24, andMizutani et al. U.S. Pat. No. 7,232,640, col. 8, line 54 to col. 12,line 14, and all other moieties and substituents defined by Allen etal., and/or Mizutani et al. For the purpose of this invention, thesemoieties and/or substituents also include combinations of moietiesand/or substituents, such as two or more of the moieties and/orsubstituents. These references give ranges of carbon atoms that apply tothe various substituents and/or moieties of this invention and thefollowing discussion applies to these ranges as well as the combinationsof moieties and/or substituents.

The invention also encompasses processes for using the compounds andcompositions of the invention to form patterned material features on asubstrate comprising a material surface which may comprise a metalconductor layer, a ceramic insulator layer, a semiconductor layer orother material depending on the stage of the manufacture process and thedesired material set for the end product. The compounds and compositionsof the invention are especially useful for lithographic processes usedin the manufacture of integrated circuits on semiconductor substrates.The compounds and compositions of the invention used in lithographicprocesses create patterned material layer structures such as metalwiring lines, holes for contacts or vias, insulation sections (e.g.,damascene trenches or shallow trench isolation), trenches for capacitorstructures, ion implanted semiconductor structures for transistors, andthe like as might be used in integrated circuit devices.

After exposure, the photoresist structure with the desired pattern isobtained (developed) by contacting the photoresist layer with an aqueousalkaline solution which selectively dissolves the areas of thephotoresist which were exposed to radiation in the case of a positivephotoresist (or the unexposed areas in the case of a negativephotoresist). Some aqueous alkaline solutions (developers) compriseaqueous solutions of tetramethyl ammonium hydroxide. The resultinglithographic structure on the substrate is then typically dried toremove any remaining developer. If a top coat has been used, it can bedissolved by the developer in this step.

The pattern from the photoresist structure may then be transferred tothe exposed portions of underlying material of the substrate by etchingwith a suitable etchant using techniques known in the art. In oneembodiment the transfer is done by reactive ion etching or by wetetching. Once the desired pattern transfer has taken place, anyremaining photoresist may be removed using conventional strippingtechniques. Alternatively, the pattern may be transferred by ionimplantation to form a pattern of ion implanted material.

Examples of general lithographic processes where the compound orcomposition of the invention may be useful are disclosed in U.S. Pat.Nos. 4,855,017; 5,362,663; 5,429,710; 5,562,801; 5,618,751; 5,744,376;5,801,094; 5,821,469 and 5,948,570. Other examples of pattern transferprocesses are described in Chapters 12 and 13 of “SemiconductorLithography, Principles, Practices, and Materials” by Wayne Moreau,Plenum Press, (1988). It should be understood that the invention is notlimited to any specific lithography technique or device structure.

Glodde et al., U.S. patent application Ser. No. ______ filed December______, 2007, Attorney Docket No. FIS920070400US1 (01400-12) describesother art-known photolithographic processes, polymers, solventsadditives and the like useful in the process and formulations of thepresent invention.

Throughout this specification, abstract of the disclosure, and in thedrawings the inventor has set out equivalents, including withoutlimitation, equivalent elements, materials, compounds, moieties,substituents, compositions, conditions, processes, structures and thelike, and even though set out individually, also include combinations ofthese equivalents such as the two component, three component, or fourcomponent combinations, or more as well as combinations of suchequivalent elements, materials, compounds, moieties, substituents,compositions conditions, processes, structures and the like in anyratios or in any manner.

Additionally, the various numerical ranges describing the invention asset forth throughout the specification also includes any combination ofthe lower ends of the ranges with the higher ends of the ranges, and anysingle numerical value, or any single numerical value that will reducethe scope of the lower limits of the range or the scope of the higherlimits of the range, and also includes ranges falling within any ofthese ranges.

The term “about,” “substantial,” or “substantially” as applied to anyclaim or any parameters herein, such as a numerical value, includingvalues used to describe numerical ranges, means slight variations in theparameter. In another embodiment, the terms “about,” “substantial,” or“substantially,” when employed to define numerical parameter include,e.g., a variation up to five per-cent, ten per-cent, or 15 per-cent, orsomewhat higher or lower than the upper limit of five per-cent, tenper-cent, or 15 per-cent. The term “up to” that defines numericalparameters means a lower limit comprising zero or a miniscule number,e.g., 0.001. The terms “about,” “substantial” and “substantially” alsomean that which is largely or for the most part or entirely specified.The inventor also employs the terms “substantial,” “substantially,” and“about” in the same way as a person with ordinary skill in the art wouldunderstand them or employ them. The phrase “at least” means one or acombination of the elements, materials, compounds, or conditions, andthe like specified herein, where “combination” is defined above Theterms “written description,” “specification,” “claims,” “drawings,” and“abstract” as used herein refer to the written description,specification, claims, drawings, and abstract of the disclosure asoriginally filed, and if not specifically stated herein, the writtendescription, specification, claims, drawings, and abstract of thedisclosure as subsequently amended.

All scientific journal articles and other articles, including internetsites, as well as issued and pending patents that this writtendescription mentions including the references cited in such scientificjournal articles and other articles, and such patents, are incorporatedherein by reference in their entirety and for the purpose cited in thiswritten description, and for all other disclosures contained in suchscientific journal articles and other articles as well as patents andthe aforesaid references cited therein, as all or any one may bear on orapply in whole or in part, not only to this written description, butalso the abstract, claims, and appended drawings of this application.

Although the inventor has described his invention by reference to someembodiments, other embodiments defined by the doctrine of equivalentsare intended to be included as failing within the broad scope and spiritof the foregoing written description and the following claims, abstractof the disclosure, and drawings.

1. A photoacid generator compound P⁺ A⁻, comprising: a) an antenna groupP⁺ comprising an atom with high EUV photoabsorption cross-sectionsaccording to FIG. 1 and A⁻ comprising an anion; or b) an antenna groupP⁺ comprising a cation commonly used in the art and A⁻, an anion withlow EUV photoabsorption cross-sections; or c) an antenna group P⁺comprising an atom with high EUV photoabsorption cross-sectionsaccording to FIG. 1 and A⁻, an anion with low EUV photoabsorptioncross-sections.
 2. The photoacid generator of claim 1 wherein A⁻comprises R—SO₃H, wherein R comprises perfluoroalkyl or substituted orunsubstituted aryl or heteroaryl groups.
 3. The photoacid generator ofclaim 1, wherein P⁺ comprises an organic chalconium cation of thegeneral structure R₁R₂R₃ Y⁺, wherein R₁R₂, and R₃ comprise aliphatic oraromatic moieties optionally containing a substituent, and Y⁺ comprisesO, S or Se.
 4. The photoacid generator of claim 3, wherein Y⁺ has a highEUV photoabsorption cross-section.
 5. The photoacid generator of claim3, wherein R₁, R₂ and R₃ comprise aliphatic or aromatic moietiesoptionally comprising at least one substituent selected from halogen,alkyl, alkyloxy, aryl, aryloxy, nitro, cyano, halogen-substituted alkylor halogen-substituted alkyloxy.
 6. The photoacid generator of claim 5,wherein the substituents R₁, R₂ or R₃ are substituted with high EUVphotoabsorption cross-section atoms selected from fluorine or iodine. 7.The photoacid generator of claim 1, wherein P⁺ comprises an organichalonium cation of the general structure R₁R₂ X⁺, wherein R₁ and R₂comprise aliphatic or aromatic moieties, and X⁺ comprises a halogen. 8.The photoacid generator of claim 7, wherein X⁺ has a high EUVphotoabsorption cross-section.
 9. The photoacid generator of claim 7,wherein R₁, and R₂ comprises aliphatic or aromatic moieties optionallyincluding at least one substituent comprising halogen, alkyl, alkyloxy,aryl, aryloxy, nitro, cyano, halogen-substituted alkyl orhalogen-substituted alkyloxy.
 10. The photoacid generator of claim 9,wherein the substituents R₁, and R₂ are substituted with atoms having ahigh EUV photoabsorption cross-section and are selected from atomscomprising fluorine or iodine.
 11. A photoacid generator compound P⁺ A⁻of claim 1 comprising: a) an antenna group P⁺ and b) A⁻ comprises anacid-forming group comprising atoms with low EUV photoabsorptioncross-sections according to FIG.
 1. 12. The photoacid generator compoundof claim 11, wherein P⁺ comprises an organic chalconium cation of thegeneral structure R₁R₂R₃ Y⁺, wherein Y⁺ comprises at least onesubstituent selected from O, S or Se and R₁, R₂ and R₃ comprise at leastone substituent selected from aliphatic or aromatic moieties optionallycomprising at least one substituent selected from halogen, alkyl,alkyloxy, alkoxy, aryl, aryloxy, nitro, alkyloxy, aryloxy, alkoxycarbonyl, cyano, halogen-substituted alkyl or halogen-substitutedalkyloxy.
 13. The photoacid generator compound of claim 11, wherein R¹and R² comprise collectively a C₂-C₃ linear or branched alkylene (CH₂),chain. R³ comprises at least one of Ar and Ar—CO—CH₂—, where Arcomprises at least one substituent selected from an aryl group,optionally comprising substituents, selected from at least one of OH,branched, linear or cyclic alkyl or branched, linear or cyclic alkyloxy,or:

wherein Ar comprising an optionally substituted aromatic group.
 14. Thephotoacid generator of claim 11, wherein P⁺ comprises an organichalonium cation of the general structure R₁R₂X⁺ wherein X⁺ comprises ahalogen and wherein R₁ and R₂ comprise aliphatic or aromatic moietiesoptionally comprising at least one substituent selected from halogen,alkyl, alkyloxy, aryl, aryloxy, nitro, cyano, halogen-substituted alkylor halogen-substituted alkyloxy.
 15. The photoacid generator of claim11, wherein A⁻ comprises the anion of a carborane orperacceptor-substituted organic anions, selected from at least onecompound comprising 4, 5, 6 or 7:

wherein E comprises an electron-withdrawing group and thering-protonation eliminates aromaticity.
 16. The photoacid generator ofclaim 15, wherein E comprises at least one of cyano (CN), alkyl,alkyloxy, hydrogen, nitro, alkoxycarbonyl, halogen, aryl, aryloxy oraryloxycarbonyl group, or atoms with low EUV photoabsorptioncross-sections according to FIG.
 1. 17. A photoacid generator compoundP⁺ A⁻ of claim 1 comprising: a) an antenna group P⁺ comprising atomswith high EUV photoabsorption cross-sections according to FIG. 1comprising an organic chalconium cation of the general structureR₁R₂R₃Y⁺, wherein R₁,R₂, and R₃ comprise aliphatic or aromatic moieties,optionally comprising at least one substituent selected from halogen,alkyl, alkyloxy, aryl, aryloxy, nitro, cyano, halogen-substituted alkylhalogen-substituted alkyloxy, fluorine, iodine, and Y⁺ comprises O, S orSe, or b) an antenna group P⁺ comprising an organic halonium cation ofthe general structure R₁R₂X⁺, wherein R₁ and R₂ comprise aliphatic oraromatic moieties optionally comprising at least one substituentselected from halogen, alkyl, alkyloxy, aryl, aryloxy, nitro, cyano,halogen-substituted alkyl or halogen-substituted alkyloxy, and X⁺comprises a halogen; c) an acid-forming group A⁻ comprising atoms withlow EUV photoabsorption cross-sections, comprised of, e.g., a carboraneor a peracceptor-substituted aromatic anion, comprising at least one copound selected from 4, 5, 6 or 7:

wherein E comprises at least one of cyano (CN), alkyl, alkyloxy,hydrogen, nitro, alkoxycarbonyl, halogen, aryl, aryloxy oraryloxycarbonyl, alkylcarbonyloxy, arylcarbonyloxy or atoms with low EUVphotoabsorption cross-section according to FIG.
 1. 18. A photoresistformulation, comprising: a) an acid-sensitive imaging polymer that isoriginally insoluble in aqueous, alkaline developers, but becomessoluble upon reaction with protons, with or without the aid of heating;b) a photoacid generator compound of claim 1; c) a small amount of abase quencher.
 19. A photoacid generator compound P⁺ A⁻, of claim 11wherein P⁺ is selected from; a) a sulfonium cation comprising,

b) and A⁻ comprises an anion having low photoabsorption cross-sectionsin EUV.
 20. A photoacid generator compound of claim 1 wherein P⁺comprises a cation having high photoabsorption cross-sections in EUV andis selected from; a) a selenium cation comprising,

b) an iodonium cation comprising,


21. The photoacid generator compound of claim 1 wherein the anion A⁻,comprises:


22. The photoacid generator compound of claim 11, wherein A⁻ comprises:


23. The photoacid generator compound of claim 1 comprising DTFPIO PFBuS.24. The photoacid generator compound of claim 1 comprising DTFPIO CN5.25. The photoacid generator compound of claim 1 comprising DTBPIO CN5.26. The photoresist formulation of claim 18 wherein said resist polymercomprises at least one of MADMA-NORLAC, ESCAP or poly([N-(trifluoromethysulfonyl)methacrylamide]-co-[2-methyl-2-adamantylmethacrylate]-co-[5-methacryloyloxy-2,6-norbornane carbolactone]), (S1).27. A method of forming a patterned material feature on a substrate,said method comprising: a) providing a material surface on a substrate;b) forming a photoresist layer over said material surface, saidphotoresist comprising (i) an acid-sensitive imaging polymer that isoriginally insoluble in aqueous, alkaline developers, but becomessoluble upon reaction with protons, with or without the aid of heating;(ii) the photoacid generator of claim 1; (iii) a small amount of a basequencher; c) patternwise exposing said photoresist layer to radiationthereby creating a pattern of radiation-exposed regions in saidphotoresist layer; d) selectively removing portions of said photoresistlayer to form exposed portions of said material surface, and etching orion implanting said exposed portions of said material, thereby formingsaid patterned material feature.
 28. A method to improve the photospeedof lithographic imaging with EUV, comprising, combining the photoacidgenerator of claim 1 with a photolithographic composition to obtain aformulation, applying said formulation to a substrate to obtain atreated substrate and exposing said treated substrate to EUV.
 29. Themethod of claim 28 wherein the photoacid generator of claim 1 comprisesthe anion A⁻;


30. The method of claim 28 to improve the photospeed of lithographicimaging, comprising combining the photoacid generator of claim 1 with aphotolithographic composition to obtain a formulation, applying saidformulation to a substrate to obtain a treated substrate, and exposingsaid treated substrate to optical lithography radiation wherein saidphotoacid generator comprises one of: